Yes, this is that same intellistation. I figured a new thread might be in order, since we're now going with the power supply as the culprit after a thorough cleaning and diagnostics run.
Interestingly enough, the system rebooted twice this morning (though not any time in the 48 hours prior), and those two reboots occurred within an hour.
As for the power supply, I obtained a 20pin ATX power supply from a colleague, and compared it to the one in the intellistation. I didn't see any additional connectors on the IBM PS, though I wasn't explicitly looking for them. Rather, I was checking to make sure that the screw holes lined up, and the wires for the main connectors on the motherboard were all the same (which they were). I'll down the system again and double check for any additional connectors on the OEM PS.
Do you remember how many pins were on the additional connector, or what it looked like?
Unfortunately the power supply I was given was only rated 300W, and was hence less useful than the 340W originally in the system.
I ordered a new StarTech 500W ATX power supply on Tuesday. We'll see when that shows up. Hopefully then the system will be reliable for the long work runs it is about to face